1. Field of the Invention
The present invention relates to a process for preparing 2-pyrrolidones by simultaneous reaction of maleic anhydride, ammonia or a primary amine and hydrogen at elevated temperature and elevated pressure in the liquid phase, using a supported catalyst containing both palladium and rhenium in metallic or bound form.
2-Pyrrolidone and, in particular, N-substituted 2-pyrrolidones are important polar solvents and extractants, for example solvents for polymers such as polyurethanes, polyimides, polyamides, polyarylene sulphides, and extractants for, for example, acetylene, butadiene, aromatics. Such pyrrolidones are also much-used media for chemical reactions (Ullmann, 4th edition, Vol. 19, Verlag Chemie 1980, p. 641-642).
2. Description of the Related Art
Maleic anhydride (MA) can be converted by hydrogenation, for instance using catalytically activated hydrogen, into succinic anhydride which can form the open-chain succinic acid in the presence of water. Furthermore, MA can be converted by hydrogenation directly or via the succinic anhydride stage into .gamma.-butyrolactone which can form the open-chain .omega.-hydroxybutyric acid in the presence of water. It is also possible to convert the .gamma.-butyrolactone into 2-pyrrolidone or into N-substituted 2-pyrrolidones by means of ammonia or primary amines. It is also possible to react MA with ammonia or primary amines in the presence of catalytically activated hydrogen to directly form 2-pyrrolidone or N-substituted 2-pyrrolidones.
The wide variety of possible reactions mentioned for MA and its downstream products, which compete with one another, make it probable that all these products are formed as a mixture if MA is simultaneously reacted with ammonia or primary amines and catalytically activated hydrogen. There have therefore been many attempts to achieve a very high selectivity in respect of the, optionally N-substituted, 2-pyrrolidones by the selection of suitable catalysts and by the gradual attainment of the individual reaction stages, which are then reacted further in steps.
CS 212 181 describes a preparation process for N-alkyl-2-pyrrolidones in which MA or succinic anhydride and a primary amine are first converted into the N-alkyl-monoamide of maleic or succinic acid which is cyclized over a hydrogenation catalyst to give the N-alkylpyrrolidone. Hydrogenation catalysts mentioned are those containing elements of groups I, II, V, VII and VIII of the Periodic Table (Mendeleev). Examples of such catalysts are Cu--Zn, Cu--Zn--Cr, Raney Ni, Raney Co; an example of a noble metal catalyst which is described is a mixed catalyst consisting of 1 g of Pt (0.2% by weight)-Re (0.1% by weight) on .gamma.-Al.sub.2 O.sub.3, 6 g of Raney Cu and 3 g of Raney Co.
In the search for a stable catalyst, German Offenlegungsschrift 24 45 871 describes a process for preparing 2-pyrrolidone in which MA is reacted with ammonia or the diammonium salt of succinic acid and, in each case, with hydrogen using a catalyst containing Ni and Re and/or Mo. The ratio of Ni to Re or Mo is 1:0.001-0.25.
A further process for preparing N-substituted 2-pyrrolidones likewise starts from maleic anhydride, maleic acid and/or fumaric acid, a primary amine and hydrogen, which are reacted in the presence of a catalyst containing Co and at least one of the elements Mn, Cu, P, Mo and/or Na (EP 460 474). This process is carried out in the presence of a solvent at elevated temperature and at elevated pressure.
Still another process for preparing N-substituted 2-pyrrolidones likewise starts from MA or maleic acid which are reacted with a primary amine in the presence of catalytically activated hydrogen. This process is further distinguished by the primary amine being able to be used in admixture with the associated secondary and/or tertiary amines and the process being carried out in the presence of water and/or ammonia. The catalyst used contains at least one element of transition groups I, VII or VIII of the Periodic Table (Mendeleev) and can additionally contain elements of transition group VI. The catalysts used in the examples are: Cu--Al.sub.2 O.sub.3 and Co--Cu--Mn--Mo--Na--H.sub.3 PO.sub.4.
U.S. Pat. No. 4,800,227 describes the preparation of 2-pyrrolidone or its N-substituted derivatives by reaction of MA with ammonia or primary amines and catalytically activated hydrogen. Use is made of catalysts containing palladium and, on a separate support, at least one element from the group consisting of ruthenium, rhodium and rhenium. The examples describe the use of a catalyst mixture which has been prepared from Ru(5%)/Al.sub.2 O.sub.3 and Pd(5%)/Al.sub.2 O.sub.3 in powder form by mixing. These two catalyst fractions are added to one another in various ratios by simple mixing. The process is carried out in a polar liquid reaction medium such as water, tetrahydrofuran or dioxane.
The patent specifications mentioned show the great sensitivity of the basic reaction towards the catalyst used. Most documents indicate that base metal catalysts, such as Raney Ni, are used more frequently than noble metal catalysts; in cases where both base metal catalysts and noble metal catalysts are used, the base metal catalyst represents the predominant proportion. When using more than one noble metal, for instance as described in U.S. Pat. No. 4,800,277, it appears important to use these metals separately from one another on different support particles.